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A pie chart is a circular chart divided into sectors, illustrating relative magnitudes or frequencies. In a pie chart, the arc length of each sector (and consequently its central angle and area), is proportional to the quantity it represents. Together, the sectors create a full disk. A chart with one or more sectors separated from the rest of the disk is called an exploded pie chart.
The earliest known pie chart is generally credited to William Playfair's Statistical Breviary of 1801.
Polar area diagram
Florence Nightingale is credited with developing an early form of the pie chart which she called the "coxcomb" which she first published in 1858. This form of pie chart is now known as the polar area diagram, or occasionally the Nightingale rose diagram. The polar area diagram is similar to a usual pie chart, except that the sectors are each of an equal angle and differ rather in how far each sectors extends from the centre of the circle. It has been suggested that most of Nightingale's early reputation was built on her ability to give clear and concise presentations of data.
Example
| Group | Seats | Percent (%) | Central angle (°) |
|---|---|---|---|
| EUL | 39 | 5.3 | 19.2 |
| PES | 200 | 27.3 | 98.4 |
| EFA | 42 | 5.7 | 20.7 |
| EDD | 15 | 2.0 | 7.4 |
| ELDR | 67 | 9.2 | 33.0 |
| EPP | 276 | 37.7 | 135.7 |
| UEN | 27 | 3.7 | 13.3 |
| Other | 66 | 9.0 | 32.5 |
Two (or more) pie charts comparing similar data can be created by ensuring that the are drawn to the same scale, using the following formula:
- (radius of b)² / number of data in b = (radius of a)² / number of data in a
External links
Sektore diagrama | Tortendiagramm | Taartdiagram | Cirkeldiagram
"Pie chart"